Method of forming superconducting ceramics by electrodeposition

ABSTRACT

The invention relates to an improvement in a method of forming deposits of superconducting ceramics. Generally, such ceramics are formed by electrodepositing a mixture of metals of the type, and in proportions sufficient to be oxidized into ceramic, onto a substrate. The electrodeposited mixture is then oxidized under conditions sufficient to result in a super conducting ceramic deposit. The improvement resides in conducting the electrodeposition in a manner which results in a patterned electrodeposition prior to conducting oxidation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to commonly assigned U.S. Appl. Ser. No.188,019 filed on even date herewith by the same inventors for "Method ofForming Superconducting Ceramics by Electrodeposition and ThinSuperconducting Ceramic Made Thereby".

BACKGROUND OF THE INVENTION

This invention relates to a method of forming films, thin films or otherlike deposits of superconducting ceramics and the superconductingceramic films made by the method. More particularly, the method isdirected to the electrodeposition of a mixture of metals of the type andin a proportion sufficient to be oxidized into a superconductingceramic, with the subsequent step of, after electrodeposition of themixture of metals, oxidizing the electrodeposited mixture of metals toform the superconducting ceramic film.

Superconducting materials, as discussed in copending application Ser.Nos. 052,830, filed in May, 1987, and 097,994, filed Sept. 17, 1987,both of which are commonly assigned, have been known since 1911.However, the synthesis of superconductors having relatively hightransition temperatures above 30° K. is a quite recent development. Bysuperconductors we herein mean such high transition temperaturesuperconductors.

One class of these materials has been found to be superconducting near90° K. and has been identified as an oxygen deficient perovskitecorresponding to the general composition MBa₂ Cu₃ O_(y) (referred tohereinafter as the 1-2-3 material), where M is La, Y, Sm, Eu, Gd, Tb,Dy, Ho, Er, Tm, Yb, Lu or Th or combinations of these elements. Twosub-classes of the 1-2-3 materials are: (a) an oxygen-reduced form, withan oxygen content of about 6.7 atoms per unit cell, which has atransition temperature (Tc) of about 60 K., and (b) a doped formreferred to sometimes as the 3-3-6 structure of general formulaM(Ba_(2-x) M_(x))Cu₃ O₇₊δ in which M=Y, La, Sm, Eu, Gd, Tb, Dy, Ho, Er,Tm, Yb, Lu or Th, where Tc ranges from 0 to about 60 K. depending on xand annealing conditions. A second independent class with a Tc ofbetween 20 and 40 K. consists of perovskite materials of compositioncorresponding to La_(2-x) M_(x) CuO₄, where M is Sr, Ba or Ca. Thesematerials have been characterized by a variety of techniques (ExtendedAbstracts of the Materials Research Society Spring Meeting, Anaheim,Calif., 1987 and "High Temperature Superconductors", Materials ResearchSociety Symposium Proceedings, Vol. 99 (1988)). More recently Bi and T1containing compositions and phases such as Bi₂ Sr₂ Ca₁ Cu₂ O₈ and T1₂Ba₂ Ca₁ Cu.sub. 2 O₈, superconducting near 110 K. and a T1₂ Ba₂ Ca₂ Cu₃O₁₀ phase superconducting near 127 K., (Proceedings of Conference onMaterials and Mechanisms of High Tc Superconductivity, Interlaken,Switzerland, 1988, to be published in Physica B.) have been identifed.

Thus, as can be seen, a lot of work has been done in superconductors,but up to now, no effective way of putting such high temperaturesuperconducting compositions to use in, for example, circuit orsuperconducting wire applications, have been developed.

More particularly, prior art methods of manufacturing superconductingcompositions involved mixing together amounts of compounds having thedesired metals in ratios as they are found in superconducting compounds,and treating the materials in a complex series of steps which ultimatelyinvolve firing in an oven to oxidize the metals into a ceramiccomposition which is superconducting (Extended Abstracts of theMaterials Research Society Symposium, Anaheim, Calif., 1987). Theresultant materials are typically powder in form and, thus, are noteasily used.

Other methods of making the superconducting ceramics involve, forexample, (i) the firing under oxygen of a metal mixture formed by moltenmetal processing and (ii) the solution deposition of an organometallicprecursor followed by a firing step under oxygen ("High TemperatureSuperconductors", Materials Research Society, Symposium Proceedings,Vol. 99 (1988)).

One prior art alternative approach to developing materials, such as the1-2-3 phase in a useable form has involved chemical vapor deposition ofthe metals. For example, in the case of the 1-2-3 composition, themetals are deposited by chemical vapor deposition, and thereafteroxidized into a ceramic film. This technique however, is complicated,and precision deposition of the film on desired areas or on desiredpaths has not yet been achieved. Moreover, the technique itself iscomplicated, requiring high vacuum, high deposition temperatures, aswell as requiring very high temperatures to fire the metals in an oxygenatmosphere to oxidize and then form the ceramic film ("Thin FilmProcessing and Characterization of High Temperature Superconductors",No. 165, American Vacuum Society Series, editors J. M. E. Harper, R. J.Colton and L. C. Feldman, 1988). The former complications are avoided bythe method of the invention.

The application of electrochemical techniques to the formation of hightemperature superconductors has been restricted to a method ofelectrochemically varying the oxygen content of certain high temperaturesuperconductors, ("High Temperature Superconductors", Materials ResearchSociety, Symposium Proceedings, Vol. 99 (1988)). No known prior artexists for electrochemically forming combinations of metals that areprecursors to high temperature superconductors. In addition, no knownprecedent exists for the electrochemical formation of combinations ofmetals similar to those found in high temperature superconductors.

In particular, there is no known precedent for the codeposition ofmetals whose deposition potentials differ by about 3V and, therefore,whose deposition rates and characteristics can be expected to differdramatically.

Those of ordinary skill in this art would not codeposit suchcombinations of metals by conventional electrodeposition methods becausesuch combinations comprise one or more metals whose deposition from anelectrolyte requires application of a highly cathodic potential (i.e.,highly reducing potential). Aqueous electrolytes, used in conventionalelectrodeposition, are, themselves, reactive with materials having suchhighly cathodic reduction potentials at these potentials. Thus, those ofordinary skill in this art would expect that such metals having highlynegative reduction potentials would not be effectively deposited on thesubstrate. By cathodic potential is meant a potential which allowselectrons to be liberated, e.g., from an electrode to reduce the chargeof a species in an electrolyte. By highly reducing potential is meantthat which is substantially negative of the potential at which H⁺ isreduced to 1/2 H₂ as at a normal hydrogen electrode (NHE). For example,each known precursor combination includes one or more metals that can bedeposited only at potentials more than 2V cathodic (negative) of NHE(e.g., Ca⁺² at potentials <-2.76V vs normal hydrogen electrode, Sr⁺² at< -2.89V, Ba⁺² at <-2.90V, Y⁺³ at <-2.37V). For comparison, copper,which is typically also required for formation of the high transitiontemperature superconductors, has a much more positive reductionpotential for Cu⁺² of +0.34 eV.

SUMMARY OF THE INVENTION

In accordance with the general aspects of the invention, a method offorming a deposit, e.g., thin films, of superconducting material, i.e.,ceramic, is provided which essentially modifies electrodepositiontechniques into a simple two-step method which results in an easilyachieved deposit, e.g., thin film, of superconducting ceramic. Likeconventional electrodeposition, the method of this invention provides ameans for forming coatings, by batch or continuous processes, on thesurfaces of irregular objects including interior surfaces, wires, andpatterned substrates. Such coatings of superconducting materials, whichcannot be conveniently obtained by alternative technologies, are ofinterest for a variety of applications such as superconductingelectrical lines, superconducting bearings, and superconducting wirewindings for magnets, transformers, and generators. The presentinvention is believed to be advantageous for the formation ofsuperconducting devices, such as SQUID's and Josephson junctions, due tothe feasibility of generating superconducting coatings in micropatternedforms.

The electrodeposition step preferably consists of applying a reducingpotential to a conductive substrate while it is in contact with anappropriate electrolyte into which are also immersed a counter-electrodeand, in some cases, other auxiliary electrodes.

In particular, the electrodeposition can be conducted from anelectrolyte containing salts of all of the metals in the mixture ofmetals to be deposited. Alternately, one or more of these metals can beincluded in the composition of a counterelectrode. Metals deposited fromthe electrolyte may include, but are not restricted to M=La, Y, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, Ba, Bi, T1, Sr, Ca, and Cu incombination and quantities sufficient to form superconducting ceramicsby oxidation. The preferred specific metals and specific proportions ofthese metals in the superconducting oxides are well described in theprior art (Extended Abstracts of the Materials Research Society SpringMeeting in Anaheim, Calif., 1987). Of course, other metals whichfunctionally behave in the same manner can be substituted for the aboveas will be readily apparent to those of ordinary skill in this art. Inaddition, other elements, which do not comprise part of asuperconducting ceramic, may be codeposited for the purpose of impartingenhanced mechanical properties. Preferred metal compositions forelectrochemical deposition and reaction to form the superconductingphase are those which are miscible, since miscibility enhances thehomogeneity of the superconductor product. Whether or not miscibilityexists is either known or readily determined for the metal system ofinterest here. Preferred elements for imparting improved mechanicalproperties are metals, such as silver, which do not substantiallyoxidize during formation of the superconductor.

Exemplary of salts that may be included in the electrolyte are:(Y(NO₃)₃, Ba(PF₆)₂, and Cu(OCOCH₃)₂. The electrolyte medium containingthe salts may be an aprotic liquid, i.e., a liquid containing minimalacidic protons, such as dimethylsulfoxide (DMSO), dimethylformamide(DMF), dimethoxyethane (DME), tetrahydrofuran (THF), and the like. Suchelectrolyte media may contain, in addition, wetting, complexing, orother agents that impart control over composition or morphology of thedeposit. Some water may also be included in the electrolyte solution inorder to achieve in some instances the desired conductivity andsolubility of the given salt. The water content would not be allowed toexceed that which would be coordinated with the dissolved ions. Suchliquids with minimal or no water area referred to as aprotic liquids. Inaddition, the electrolyte medium may be an ion-conducting conductingpolymer, such as salt-containing polyethylene oxide, or a fused salt orfused salt mixture.

The potential applied to the substrate should be sufficient to reducecations of each salt in the electrolyte to its neutral oxidation state.It should, therefore, be sufficiently cathodic (i.e., at a suitablyreducing potential) to reduce the cation having the most negativereduction potential of the mixture. For example, codeposition from anelectrolyte containing salts of Eu, Ba, and Cu, requires the applicationof potential <-2.89V versus normal hydrogen electrode in order to reduceBa(+2) to Ba(0) (standard reduction potential -2.89V) as well as Cu(+2)to Cu(0) (+0.34V), and Eu(+3) to Eu(0) (-2.37V). The applied potentialmay be varied with time, pulsed, or periodically reversed in order toregulate deposition current, electrolyte composition, and depositnucleation.

According to the method of this invention, the mixture of metals iselectrodeposited onto a substrate which is electrically conductive andnot harmful to the resultant ceramic. Electrode substrate materials maybe metallic, semiconductive, or photoconductive. They may be freestanding such as conductive plates, rods, wires, fibers, and foils, orsupported by structural material such as conductive thin films ofmetals, conductive oxides, and semiconductors coated on quartz andceramics. The electrode substrates may be virtually any size, shape, andnumber as long as the electrolyte in contact with the surfaces to becoated is also in contact with a counter electrode. The electrodesubstrate can consist of or include a metal or metal containingcomposition which reacts with the electrodeposited metal duringoxidation to form the superconductor. For some applications it isdesirable to utilize the electrode substrate as the sole source of oneof the metals required for formation of the superconductor. Thisrequires interdiffusion of substrate and deposited metals. For purposesof such interdiffusion, post-deposition thermal annealing is useful. Apreferred example is electrodeposition of all the metals in thesuperconductor except for copper onto a low denier copper wire or thincopper foil. Oxidation of the substrate containing electrodepositedmetals then yields the superconductor in wire or foil form. For thepurpose of obtaining oriented growth of the superconductor phase, andthereby obtaining enhanced critical currents, substrate electrodegeometries which provide preferential crystal growth directions can beused. One such convenient substrate electrode geometry is obtained bygrooving the electrode surface with parallel lines. The substratematerial can also be chosen as one which will disappear via sublimationor gasification under the oxidation conditions, so as to result in asubstrate-free superconductor.

The counter electrode and other auxiliary electrodes useful in thismethod are electrically conductive solids such as metals,semiconductors, and photoconductors. They may be inert or electroactiveunder the conditions of electrodeposition. Those that are electroactivemay be useful as sources to the electrolyte of cations of metals beingdeposited. Counter electrodes with high electrical conductivities (above100 S/cm) are preferred in order to minimize resistive energy lossesduring electroplating.

The electrodeposition of the metal mixtures may be performed in secondsto several hours, depending on the deposition current which may rangefrom about 10⁻³ to about 10⁺³ mA/cm² of substrate area. The preferredcurrent for deposition from aprotic liquid electrolytes is from about10⁻² to about 10 mA/cm². The film thicknesses may range from about 10⁻²to about 10⁺³ microns or more. The preferred film thicknesses range fromabout 10⁻¹ to about 100 microns. Electrodeposition of precursor metalmixtures must be conducted at temperatures wherein the electrolyte isionically conductive. Electrodeposition in aprotic liquid electrolytesis conducted, generally, at temperatures between about -40° and about+200° C. The preferred temperature range for using aprotic liquidelectrolytes is from about 0° to about 100° C. Solid polymerelectrolytes are generally useful between about 60° and about 300° C.,and fused salt electrolytes are generally useful between about 200° andabout 500° C. Due to higher obtainable conductivities, aprotic liquidelectrolytes and fused salt electrolytes are preferred over solidpolymer electrolytes. Due to convenient operation near room temperature,aprotic liquid electrolytes are most preferred.

The compositions of deposited mixtures are generally dictated bydeposition currents of the individual species at a given appliedpotential, relative salt concentrations in the electrolyte, and totalsalt concentration. In the case of aprotic liquid electrolytes, appliedpotentials are configured to those that are sufficient to deposit alldesired species but not so highly cathodic as to harm the depositthrough decomposition of the electrolyte. Relative deposition currentsof the individual species, which may differ greatly for a given mixture,are, therefore, similarly restricted. In addition, total saltconcentration is restricted by solubilities in a given electrolytemedium. Adjustments to salt concentrations in the electrolyte are,however, effective in obtaining desired deposit composition. Thismethod, therefore, includes a process for establishing the dependence ofdeposit composition on relative salt concentrations known to those ofordinary skill in the art. For example, at an applied potential of -5V(vs Ag/Ag⁺) and a total salt concentration of 0.1M in DMSO, Y-Ba-Cu inthe deposit varied according to relative cation concentrations asfollows:

    ______________________________________                                        Composite      Electrolyte                                                    Y      Ba        Cu    Y.sup.+3 Ba.sup.+2                                                                          Cu.sup.+2                                ______________________________________                                        1      1.1       9.7   1        2    1                                        1      1.4       3.1   1        2    0.5                                      1      1.8       3.4   1        2.8  0.5                                      ______________________________________                                    

Finally, the invention also relates to a superconducting film on asubstrate made in accordance with the method of the invention. Further,although the invention has generally been discussed with respect to theyttrium or europium, barium, copper 1-2-3 composition, it is clear thatthis electrodeposition technique and later oxidation can be applied toother superconducting compositions such as, for example, that disclosedin copending application Ser. No. 097,994, referred to as the 3-3-6,yttrium, barium, copper composition, and T1₂ Ba₂ Ca₁ Cu₂ O_(x) and T1₂Ba₂ Ca₁ Cu₃ O_(x) compositions.

BRIEF DESCRIPTION OF THE DRAWINGS

Having briefly described the invention, the same will become betterunderstood from the following detailed discussion, taken in conjunctionwith the drawings wherein:

FIG. 1 is a comparison of the X-ray diffraction pattern of a filmdeposited from a DMSO solution of Eu(NO₃)₃, Ba(NO₃)₂ and Ca(OCOCH₃)after oxidation thereof (top) with the x-ray diffraction patternpreviously established for a superconducting phase of Eu-Ba-Cu-O and twoimpurity phases (Y₂ BaCuO₅ and CuO);

FIG. 2 is a magnetic susceptibility graph as a function of temperatureof EuBa₂ Cu₃ O_(7+x) formed by oxidation of an electrodeposited mixtureof Eu, Ba and Cu;

FIG. 3 is a magnetic susceptibility graph as a function of temperatureof the oxidized Bi, Sr, Ca and Cu-containing film of Example II herein;and

FIG. 4 is a schematic diagram of two continuous electrochemicalprocesses.

DETAILED DISCUSSION OF THE INVENTION

In accordance with the invention, metal mixtures are electrodepositedonto substrates and oxidized to form films of superconducting ceramics.More particularly, electrodeposition of appropriate metals is performedsimultaneously from a single electrolyte. The oxidation is thengenerally performed by heating the deposited metal mixture in anoxygen-containing atmosphere.

The principal advantage provided by this method is that a facile andversatile technique for incorporating elements into circuits, which canthen be converted to a superconducting composition, is provided. Theelectrochemical technique is performed in a single step requiringneither the high temperatures necessary for metallurgical deposition ofthe metals nor the high vacuum required for chemical vapor or molecularbeam deposition techniques. The selection and number of metals that maybe electrodeposited is not restricted by the method, the onlyconsideration being that it must include those metals in a ratio whichcan be oxidized to form a superconducting ceramic. Thus, thestoichiometry and thickness of the metal deposited is controlled inaccordance with conventional electrodeposition methods.

Exemplary of metal mixtures which are formed and subsequently oxidizedaccording to this method are mixtures: Eu or Y, Ba, and Cu in a 1-2-3ratio; Bi, Sr, Ca, and Cu in a 1-1-1-2 ratio; and T1, Ca, Ba, and Cu ina 1-1-1-2 ratio.

Typically, the electrodeposition is conducted at room temperature from aliquid electrolyte comprised of salts of the metals dissolved in anaprotic solvent by applying a voltage across the substrate andcounter-electrode such that the substrate is held at a constantpotential of about -3 to about -6V versus a Ag/Ag⁺ reference electrode.The concentrations of the salts are adjusted to account for the relativedeposition rates of the different cation species. For example, Y, Ba,and Cu are deposited in a ratio of 1-2-3 onto an In-Sn oxide film onquartz substrate when a potential of about -5V versus Ag/Ag⁺ is appliedto the substrate immersed in a DMSO solution that is about 0.1M inY(NO₃)₃, about 0.27M in Ba(NO₃)₂, and about 0.05M in Cu(OCOCH₃)₂. As asecond example, Bi, Sr, Ca and Cu are deposited onto a Pt substrate whena like potential is applied to the substrate immersed in a DMSO solutionthat is about 0.02M in Bi(NO₃)₃, about 0.1M in Sr(NO₃)₂, about 0.092M inCa(NO₃)₂ and about 0.025M in Cu(OCOCH₃)₂. After passage of about 0.1 toabout 40 coulombs/cm² for typical films having thickness of about 0.1micron to about 40 microns, i.e., 1 micron per coulomb, the substratewith deposited film is removed, rinsed in fresh solvent, and dried.

Since the electrodeposition process can function as a purification stepto eliminate undesireable impurities in the metal salts, this presentprocess for forming the superconductors can utilize effectively lowerimpurity precursors than are possible for alternate fabricationtechniques for thin film formation, such as sputtering.

Once it is confirmed that that deposit consists of the metals inquestion in the preferred yield, the substrate is then heated in anoxidizing atmosphere up to a temperature and time sufficient to oxidizethe deposited metals into the superconducting ceramic state. Eitherprior to or following this oxidation step, it is sometimes desirable toutilize other thermal or chemical treatments known in the art in orderto enhance the properties of the superconductor. For example, meltingand resolidification of the as-formed superconductor can be employed toprovide enhanced critical currents via enhanced preferential alignmentof crystallite grains in the superconductor.

As a refinement, this procedure can be employed in combination withother technologies to produce patterned superconducting films. Forexample, electrical circuits and other objects containingsemiconductors, insulators, or conductor elements with superconductingpaths may be formed by this method in combination with conventionallithography or in combination with photoinduced enhancement ofelectrodeposition. Such combinations can be particularly useful informing parallel arrays of superconducting wires and dots such as thoseuseful as high efficiency transparent shields of electromagneticradiation. For applications in which high spatial resolution is notrequired for the superconductor elements of a circuit or array,patterned superconductor films can arise from electrodeposition usingpatterned counterelectrodes. As a further refinement, the procedure canbe employed in a continuous manner using continuous substratesconfigured, for example, about a "rotating drum" or rotating beltcathode (see FIG. 4).

Selective area electrochemical deposition of the superconductorprecursor alloys can be conveniently accomplished using a modificationof the lithography techniques conventionally employed to form circuitsof metallic and semiconducting elements. An insulating photoresist isdeposited (for example, by solution or gas deposition) on the electrodesubstrate. In one embodiment, a positive photoresist is made insolubleor nonvolatile as a consequence of selected area irradiation, so thesubstrate conducting electrode is later revealed (after solvent orthermal treatment) only in those regions of the electrode where thephotoresist has not been irradiated. Since only the nonirradiatedregions of the electrode are not insulating, only those regions undergodeposition of the alloy upon electroplating. Alternately, theirradiation process can lead to either enhanced solubility orvolatilization of the irradiated regions of the photoresist. In theformer case, solvent treatment of the irradiated electrode can be usedto expose the conductor surface only at irradiated regions of thephotoresist. Upon subsequent electroplating, the superconductorprecursor alloy forms only on portions of the electrode where theinsulating layer of photoresist has been removed.

The metal alloy composition which is precursor to the superconductor canalso be electrochemically deposited in a patterned form on an electrodeusing photoinduced inhancement of electrochemical deposition. For thispurpose, the most convenient photon source is a higher energy laserwhich is scanned across the electrode surface to generate the patternedalloy deposition. Depending upon the selected photon frequency, theelectrolyte, and the target electrode surface, the mechanism of thephotoenhanced electrochemical deposition varies. For example, relativelylow photon fluxes can be used to generate photocarriers in aphotoconductor present at the electrode surface. The resulting currentflow through the photoconductor then generates the patterned alloydeposition. Alternately, the photon source can provide patterned alloydeposition by selective volume heating of either the electrolyte or theelectrode surface, so as to provide increased current flow at points ofirradiation. High temperature oxidation and thermal annealing transformsthe patterned alloy deposition into a patterned superconductordeposition. Patterned deposition on a photoconductor surface can alsoresult from patterned exposure to penetrating radiation, such as x-rays.Hence, it is possible to generate a patterned deposition of thesuperconductor on surface areas which are inaccessible to either visibleor ultraviolet radiation.

For applications in which high spatial resolution is not required forthe patterned formation of superconductor on a substrate, it is possibleto utilize an alternate strategy for patterned deposition. Specifically,the use of a patterned counter electrode or patterned motion of acounter electrode (having dimensions much smaller than the patterndesired on the electroplated electrode) can be used for theelectroplating of the precursor superconductor alloy. Note also thatsegmentation of the patterned counter electrode, so as to providesubunits in the pattern which are at different voltages, provides anadditional design feature for the patterned electroplating of theprecursor superconductor alloy. This effective segmentation can beeither by direct electrical separation or by the use of internalresistive elements. Similarly, use of a counter electrode whichundergoes voltage changes during patterned motion provides additionalflexibility for the electrochemical deposition of a patternedsuperconductor precursor alloy.

Modification of the above-described photoenhanced electrochemicaldeposition can be used to conveniently generate parallel superconductingwires having separations comparable with the wavelength of light. Themodified approach utilizes the alternating stripes of intense light andnear-zero light intensity resulting from the interference of two lightbeams. This pattern of illumination generates, via selected areaphotoenhancement of current flow, the patterned deposition ofsuperconductor precursor alloy. Note that oxidation of the therebyobtained precursor alloy wires can provide the additional advantage oforiented growth of the superconductor as a consequence of the shapeanisotropy of the precursor alloy. Such oriented growth is preferred forimproving the properties of the superconductor, and specifically forincreasing the critical amount.

Patterned electrochemical deposition of the superconductor precursoralloy on a transparent electrode substrate, using the above-describedmethods, permits preparation of an optically transparent superconductor.The patterning, such as an array of parallel strips or a two-dimensionaldot array of either the superconducting or the superconductor-freeareas, provides for optical transparency. Such transparent films canfind applications as windows which have extremely high efficiency forthe shielding of radio frequency and microwave frequency radiation. Useof a two-dimensional dot array of superconductor can provide for a filmwhich is superconducting in the film thickness direction and insulatingin the plane of the film.

The electrode electroplated with the superconductor precursor alloy canbe in the form of a moving belt or wire which passes continuously intothe electroplating solution and into close proximity to the counterelectrode. (Passage of the wire through the center of a cylindricalcounter electrode is preferred in the latter instance.) If desired, thebelt (or wire) can then pass from the electroplating solution into achamber for thermal treatment in an oxygen-containing atmosphere. Thisthermal treatment in oxygen to provide the high temperaturesuperconductor can employ an oxygen plasma or laser-induced heating. Ifthick coatings of the superconductor are desired, the belt (or wire) canpass continously between the electroplating bath and the oxidationchamber. Analogously, thick coatings of superconductor can be formed ona drum-shaped article by rotation of a drum-shaped electrode so thatelectroplating continuously occurs on the side of the drum which isimmersed in the electroplating solution. The opposite side of the drumcan be continuously laser heated in an oxygen-containing atmosphere totransform the metal alloy into a superconductor. Similarly,electrodeposition can be on a disk shaped counter electrode which iscontinuously rotated, so as to expose a continuously varying surface ofthe disk to electroplating process.

The rotating drum method can be employed for the direct fabrication of aspiral-like wind of superconducting and insulating sheets. Upon nearcompletion of a 360° deposition of the superconducting layer, processingconditions can be changed so that near 360° deposition of an insulatoris applied. Alternation of the processing conditions which result in theinsulator and the superconductor, so as to maintain continuity in thesuperconductor sheet, results in the winding of the magnet. The changesin processing conditions can correspond to changes in the appliedelectrochemical potential, changes in the composition of theelectrochemical bath, and/or changes in the heat treatment environment,so as to result in the change from formation of superconductor toformation of insulator. Alternately, the insulator layer can be appliedby more conventional routes, such as sputtering a layer of insulatingoxide.

In contrast with the conventional technology of forming thin films bysputtering, the electrochemical approach is well suited for depositionof the superconductor precursor alloy on complicated shapes and interiorsurfaces of articles. For example, the precursor alloy to thesuperconductor can be deposited on the inside surface of a pipe byfilling the pipe with electrolyte, centrally located the anode in thepipe, and utilizing the inner surface of the pipe as the cathode forelectrochemical deposition. Transformation of the precursor alloy intothe superconductor is then conveniently accomplished by heat treatmentof the pipe in an oxygen-containing atmosphere.

Having generally described the invention, the following examples areintended to be illustrative but not limiting any manner.

EXAMPLE I

Europium, barium, and copper were codeposited by electrodeposition ontoa platinum foil electrode in a molar ratio of 1-2-3. The platinum foilelectrode, a copper counter electrode, and a Ag/Ag⁺ reference electrodewere immersed in a dimethylsulfoxide solution that was 0.1M in Eu(NO₃)₃,0.27M in Ba(NO₃)₂, and 0.051M in Cu(OCOCH₃)₂. A constant potential of-5.0V versus the Ag/Ag⁺ electrode was applied to the platinum electrodeand a deposit formed on the platinum electrode. After 11 coulombs/cm²had passed, the platinum electrode was removed, rinsed in fresh DMSO anddried. A portion of the deposition was shown by electrode microprobeanalysis to be composed of Eu, Ba, and Cu in the approximate ratio1-2-3. A second equivalent portion was heated to about 900° C. for about15 min in an atmosphere of dry oxygen to yield a gray-black film inplace of the deposited metals. This film exhibited an x-ray diffractionpattern identical to that of previously synthesized superconductingceramic EuBa₂ Cu₃ O_(7+x) (FIG. 1). In FIG. 1 all of the peaks can beassigned to either the 1-2-3 phase (shown for EuBa₂ Cu₃ O_(7+x)) or tothe impurity phases Eu₂ BaCuO₅ (known as the "green phase") and copperoxide. Magnetic susceptiblity measurements of the black film indicated asuperconducting transition at 60° K. (FIG. 2).

EXAMPLE II

Bismuth, strontium, calcium and copper were codeposited onto a platinumfoil electrode in a ratio of 0.2-0.2-1-2 following the procedureoutlined in Example I. Ten coulombs were passed while a potential of -4Vvs a Ag/Ag⁺ reference electrode was applied to the platinum electrodewhile the substrate was immersed in a DMSO solution of 0.02M Bi(NO₃)₃,0.1M Sr(NO₃)₂, 0.092M Ca(NO₃)₂, and 0.025M Cu(OCOCH₃)₂. A smooth filmcomprised of tightly packed micro spheres resulted, each sphereconsisting of the four elements. The film was then oxidized to thesuperconducting ceramic by heating in a dry oxygen atmosphere at 850° C.for 15 minutes. Magnetic susceptibility measurements of the oxidizedfilm on Pt indicated a superconducting transition at 80° K. (FIG. 3).

EXAMPLE III

Yttrium, barium and copper were codeposited by electrodeposition onto aplatinum foil electrode in a ratio of 1:2:3. The platinum foil electrodeand a copper counter electrode were immersed in a dimethyl-sulfoxide(DMSO) solution of 0.21M Y(NO₃)₃, 0.057M Ba (NO₃)₂, and 0.001M Cu(OAc)₂. A constant potential of -4.0V to -5.0V, as compared to a silverwire reference electrode, was applied to the platinum foil electrode anda deposit was formed on the platinum electrode. After 10 coulombs/cm²had passed (approximately 20 minutes), the platinum electrode wasremoved, rinsed in fresh DMSO and dried and analyzed by the electronmicroprobe technique. The analysis indicated that the deposit consistedof Y, Ba and Cu in the ratio of roughly 1:2:3. The electrode thereafterwas heated to about 900° C. for about 5 minutes to yield a black film inplace of the deposited metals. The black film exhibited an x-raydiffraction pattern identical to that of the previously prior artsynthesized superconducting ceramic YBa.sub. 2 Cu₃ O_(7-x).

EXAMPLE IV

Yttrium, barium, and copper were codeposited in different ratios, ontoconductive indium-tin oxide films supported on quartz, from DMSOelectrolytes having different relative concentrations of Y(NO₃)₃,Ba(NO₃)₂, and Cu(OCOCH₃)₂. In each case, the total ion concentration wasabout 0.05 to about 0.1M, the potential applied to the substrate was -5Vversus Ag/Ag⁺, and about 2 to about 10 coulombs were passed duringelectrodeposition. After each deposition, the composition of the depositwas determined by electron microprobe analysis. Representativeelectrolytes and compositions of their resulting deposits are shownbelow.

    ______________________________________                                        Electrolyte        Composite                                                  Y.sup.+3                                                                              Ba.sup.+2  Cu.sup.+2                                                                             Y       Ba  Cu                                     ______________________________________                                        1       2          1       1       1.1 9.7                                    1       2          0.5     1       1.4 3.1                                    1       2.8        0.5     1       1.8 3.4                                    ______________________________________                                    

EXAMPLE V

Europium, barium, and copper were codeposited in a molar ratio of about1-2-3 onto the interior surfaces of cylindrical copper tubes havinginternal diameters of 2, 4, and 6 mm. Each tube was fitted with a copperwire counter electrode held in the axial position of the tube by aporous separator of hydrophylic polypropylene (Celgard ). After fillingeach tube with the electrolyte of Example I, a potential of -5V versusits copper counter electrode was applied to the tube. In each case, acontinuous film covering the internal surfaces of the tubes were formed.Samples of the films scraped from the tubes were shown by microprobeanalysis to contain Eu, Ba, and Cu in a ratio of about 1-2-3.

EXAMPLE VI

Bismuth, strontium, calcium, and copper were codeposited onto carbon matin a ratio of about 0.2-0.2-1-2 following the procedure of Example IIexcept that about 100 coulombs per cm² were passed during electrolysis.A film of the electrodeposited metals covered the carbon fibers.Oxidation of the coated carbon mat by heating at 850° C. for 15 minutessubstantially removed the carbon fibers leaving behind a continuousnetwork of ceramic fibers.

EXAMPLE VII

Selected area electrochemical deposition of the superconductor precursoralloys is accomplished by modifying conventional lithographic techniqueswhich are conventionally employed to form circuits of metallic andsemiconducting elements. An insulating photoresist is deposited byeither solution or gas deposition on the platinum electrode substrate. Apositive photoresist is made insoluble by selected area irradiation, sothat the substrate conducting electrode is later revealing (aftersolvent or thermal treatment) in those regions of the electrode wherethe photoresist has not been irradiated. Thereafter, the electrode iselectro-deposited as in Example I and only those regions, i.e., thenon-irradiated regions of the electrode which are not insulating,undergo deposition of the alloy or metals upon electroplating. Uponsubsequent electroplating, the superconductor precursor alloy forms onlyon the portions of the electrode where the insulating layer ofphotoresist has been removed. Thereafter, the oxidation is conducted inaccordance with Example I.

EXAMPLE VIII

A metal alloy composition which is precursor to the superconductor ofExample I, is electrochemically deposited in a patterned form on anelectrode using photo-induced enhancement of electrochemical deposition.The photon source is a high energy laser which is scanned across theelectrode surface to generate the patterned alloy deposition. Theselected photon frequency, electrolyte, electrode potential and targetelectrode surface is varied to control the rate of the photoenhancedelectro-chemical deposition to a predetermined value. Thereafter hightemperature oxidation, i.e., at about 900° C., and thermal annealing, atabout 650° C. is employed to transform the patterned alloy depositioninto a patterned superconductor film.

EXAMPLE IX

The method of Example V is modified to generate parallel superconductingwires having separations comparable with the wavelength of the lightemployed in the photo deposition. The approach utilizes alternatingstripes of intense light and near zero light intensity resulting fromthe interference of two light beams appropriately positioned. Thepatterned illumination generates, through selected areaphoto-enhancement of current flow, the patterned deposition ofsuperconductor precursor alloys. The oxidation of the thereby obtainedprecursor alloy wires provides oriented growth of the superconductorduring oxidation as a consequence of the shape anisotropy of theprecursor alloy. This preferred growth improves the properties of thesuperconductor with the oxidation being accomplished, into thesuperconducting state, in accordance with the method of Example I.

EXAMPLE X

Deposition of the superconductor precursor alloys on the inside of ametal tube and on the surface of a metal wire is accomplished byelectrochemical techniques similar to that described in examples I andII. Thereafter the oxidation to superconducting ceramic is conductedalso in accordance with the processes described in examples I and II togive a wire and the inside of a tube coated with superconductingmaterial.

What is claimed is:
 1. In a method of forming deposits ofsuperconducting ceramics comprising the steps of (a) electrodepositingonto a substrate a mixture of metals, of the type and in proportionssufficient to be oxidized into ceramic, and (b) oxidizing saidelectrodeposited mixture on said substrate, under conditions sufficientto result in a superconducting ceramic deposit, the improvement whereinthe electrodepositing step is conducted in a manner such that apatterned deposit results, with said oxidation step being conducted onsaid patterned deposit to result in a patterned superconducting deposit.2. A method as in claim 1 wherein patterned deposition is inconducted bylithographically depositing a photoresist in a patterned manner on saidsubstrate, and thereafter conducting said electrodepositing step.
 3. Amethod as in claim 2 wherein said deposited photoresist is a positivephotoresist, and further comprising making said positive photoresistinsoluble or nonvolatile by selective area irradiation, thereaftertreating said substrate to reveal the non-irradiated regions, andthereafter conducting said electrodepositing step.
 4. A method as inclaim 1 wherein said electrodeposition is conducted by photoinducedenhancement.
 5. A method as in claim 4 wherein said photoinducedenhancement of electrodeposition is conducted by scanning a photonsource across the substrate surface to generate patterned deposition. 6.A method as in claim 5 wherein said photon source is a laser.
 7. Amethod as in claim 1 wherein said substrate is an electrode, and saidpatterned deposition is conducted by the use of a patternedcounter-electrode.
 8. A method as in claim 1 wherein said substrate isan electrode in the form of a moving belt, and wherein saidelectrodeposition is conducted by passing the moving belt continuouslythrough a bath of electroplating solution while establishing a potentialbetween the moving belt electrode and a counter-electrode.
 9. A methodas in claim 1 wherein said substrate in an electrode in the form of amoving wire, and wherein said electrodeposition is conducted by passingthe moving wire continuously through a bath of electroplating solutionwhile establishing a potential between the moving wire electrode and acounter-electrode.
 10. A method as in claim 1 wherein said substrate isan electrode in the form of a rotating disk or rotating cylinder, andwherein said electrodeposition is conducted by rotating the rotatingdisk or rotating cylinder continuously in a bath of electroplatingsolution while establishing a potential between the rotating disk orrotating cylinder electrode and a counter-electrode.